Replies

1. 
   Matt | Jun 02, 2010 07:39am | #1

   None that I can think of other than installing another post.

   You are proposing:

   _____________  _______________

   _____________  _______________

   x                         x                             x

   _____________  _______________

   _____________  _______________

    

   I am suggesting:

   ________  ___________________

   x               x               x                    x

   _________________  ___________

    

   Either that, or go to a real lumber store and get some 20'ers.

1. 
   davidmeiland | Jun 02, 2010 08:58am | #2

   Terrible idea

   to use (4) 2 x 8. The "wood sandwich" will hold water in between the layers of 2x and will rot out. The butt joint in the middle will be the worst spot.

   Go to a real lumber store and get a 4 x 8 - 20. Buy a roll of Vycor Deck Protector and lay a strip along the top of the beam before you lay the joists across it.

1. 
   junkhound | Jun 02, 2010 12:10pm | #3

   Go to a real lumber store and get a 4 x 8 - 20

   Ya beat me to it,   why in the world would anybody scab together 4 ea 2x10 to make a simple 4x8!

   Or, unless you need headroom under the deck, a single 20 ft  PT  2x12.  --  which is 20% stronger than 2 sister 2x8s,  AND lower cost (in some localities) and less 'envrionmental impact .'

1. 
   Matt | Jun 02, 2010 04:17pm | #4

   4x8?

   It may interest you to know that those kind of timbers are not normally used is my area - the SE usa - Not saying they are not available - although I'd have to look real hard for a 20'er, I'm just saying the use of those kind of beams is nor normal stuff in many parts of the country.  Here, every wood girder we install is a bulti ply afair.  It may have something to do with the fact the the PT lumber you all in the Pac NW get is cr@p....

   Re the single 2x12, again here, that wouldn't pass inspection in ANY of the juresdictions in which I build.

1. 
   davidmeiland | Jun 02, 2010 08:49pm | #5

   Even here in podunk

   I can drop by the yard and buy a 4x8-20 PT any day of the week. The 2x stuff tends to be somewhat wanky hem-fir, the 4x stuff is more likely fir.

   No real problem with multi-ply beams but I would flash the top with Vycor.

2. 
   Matt | Jun 03, 2010 08:16am | #6

   Flashing is good...

   Here a 4x8-20’ would be a special order - and BTW - I deal with massive building supplies.  Or at least they were massive until this building downturn...  I used to see like 6 carloads (as in train cars) of OSB sitting on one of their yard's waiting to be unloaded.  Like I said the 4x8 thing is a regional thing.  Here 4x8xanything just aren’t used unless you are going for a specific look – like maybe for an arbor or something.  I remember reading Larry Haans framing book where he talked about using such lumber for headers….  Never seen that around here.  Really I suspect that the everyday use of such material is limited to west of the Rockies– but don’t know that for a fact.  Here the defacto PT material is SYP which takes the PT chemicals very well.  I think that might be the standard east of the Mississippi but again, don't know that for a fact.  Here at BT I’ve seen pics of that west coast “incised” lumber that is done like that to try and get it to absorb the PT chemicals – never seen that stuff around here.  Also, what large dimension lumber we do get here tends to check pretty bad - maybe the SYP thing...

   The flashing is a really good technique though, especially for example, for that guy in the other thread who is building an ipe deck and therefore needs something that will last a really long time.  I've removed 15 YO decks on which the tops of the joists and beams had gone soft from water sitting on them.  Who knows how long the AZQ stuff will last - although I guess we are coming up on 10 years on that...

   Back to the initial post, without looking it up I'd say that a 2 ply 2x8 beam wouldn't span 10' anyway.  The PSF requirements for decks vary by state though...  Also, the statement of “the bill of the materials state that my beam is made of 4 2x8x10 "  struck me as a little weird.... What ever happened to figuring out how to build something and then making a material list? J

   As a little side note my great grandfather was a real estate & lumber dealer in WA state back around 1900.  Shocking to see how few of the big trees are left these days....  I guess same goes for east coast, it's just been more centuries since the big ones were wiped out...

2. 
   Piffin | Jun 04, 2010 06:56am | #7

   Sounds like a Home depot pop-up-knock-down deck to me. I would not be trying to span ten feet with only 7,25" deep "beam" - maybe in Florida where there is no snow load...

1. 
   ki | Jun 05, 2010 10:46pm | #8

   i agree

   with piffin, the beam sounds thin, at least for my area in ontario. as someone else suggested dont use two butt joints together over the middle post, overlap the joints halfway.  definitely protect the top of the beam with a membrane of some sort, the water will get between the boards and really rot quick. if you look at the end of the acq treated boards, the treating chemical barely breaks the surface on some boards. look into a new product called timbersil.

2. 
   Kevin_D | Jun 09, 2010 10:02pm | #9

   Funny you say that. Every time I cut a PT board, I think how thin the layer of treated wood looks. 

2. 
   JohnSprungX | Jun 22, 2010 06:22pm | #10

   How high up is this?

   That's a question to ask on every deck project.  If this is a first floor deck where you're just 2-3 feet off the ground, make use of the handy nearby planet and put in lotsa posts, like 4 or 5, to reduce your spans. 

   If this is an upstairs deck where you're going to want to walk around underneath, posts are a pain.  Consider going with steel, say 5" diameter posts and W14x22, so you only have two corner posts to dodge. 

   -- J.S.